Stabilization of photographic prints with thiocyanate

ABSTRACT

A process for the stabilization of photographic images includes subjecting a developed silver halide emulsion layer containing the silver images to thiocyanate stabilization and then laminating an organic colloid layer containing a heavy metal salt on a transparent support to the surface of the emulsion layer. Highly stable glossy prints are obtained.

United States Patent Inventor Henry J. Fassbenden Rochester, N .Y.

Appl. No. 740,475

Filed June 27, 1968 Patented Oct. 26, 1971 Assignee Eastman Kodak Company Rochester, N.Y.

STABILIZATION OF PHOTOGRAPHIC PRINTS WITH THIOCYANATE 8 Claims, No Drawings US. Cl .l .o 96/50, 96/29 Int. Cl G03c 5/26 Field of Search 96/50 [56] References Cited UNITED STATES PATENTS 2,866,705 6/1953 Land 96/50 PL FOREIGN PATENTS 775,322 2/1955 England 96/50 PL Primary Examiner-Norman G. Torchin Assistant Examiner-John L. Goodrow Attorneys-Walter O. Hodsdon, Paul R. Holmes and Wendell H. McDowell processes residual undeveloped silver halide is usually converted to a compound more stable to heat, light and moisture than silver halide. In a useful stabilization process a solution containing thiocyanate, especially ammonium thiocyanate, is used to stabilize the layers containing silver images and thus avoid the fixing and washing steps. Further time is saved by not ferrotyping the stabilized prints. However, this results in lack of surface gloss and thus lower definition in the silver images. In addition, the silver images are not as stable as is desirable.

I have discovered that when a transparent sheet carrying a hydrophilic organic colloid layer is laminated to the surface of the thiocyanate stabilized layers not only is a glossy protective surface obtained but silver images have improved stability. More particularly, if a heavy metal salt, such as a zinc salt, has been incorporated into the organic colloid layer, a considerable increase in stability of the silver images is obtained.

It is known to laminate a transparent sheet to a photographic layer containing a silver image as shown by U.S. Pat. No. 2,798,021, using an adhesive solution containing a metal salt for effecting lamination of the transparent sheet to the layer containing the silver image. In that process the metal salt is used to protect the silver image from sulfides in the atmosphere. The process of my invention is distinct from that process in that the organic colloid layer which is laminated to the image layer contains a metal salt apparently to prevent interaction of the silver image with thiocyanate present in the image layer. The process does not appear to be effective where developed emulsion layers have been stabilized by other methods, for example where thiosulfate has been used. Also, compared to the process of the patent it is not necessary to providea separate adhesive composition for laminating the transparent sheet to the silver image and, thus, any excess adhesive'does not have to be removed from the prints and apfparatus- In my process it is possible to use only the moisture in the freshly processed layer containing the silver image, or slight additional moisture, to cause the transparent sheet to adhere. Moreover, in my process the metal salt such as a zinc salt is incorporated into a solution of hydrophilic, organic colloid such as gelatin before coating the gelatin layer on the transparent support. Thus, the salt can be more effectively and uniformly dispersed in the layer than, for example, by bathing the layer with a salt solution before laminating it to the silver print.

An unexpected feature of my process is that such high print stability is obtained. Also, it is unexpected that a very clear picture is obtainable by laminating the colloid layer to the emulsion layer containing the silver image without use of an adhesive containing film-forming material. As mentioned, lamination is obtained by means of moisture.

The photographic elements providing the silver images to be stabilized are well known in the art. Conventional hydrophilic organic colloid silver halide emulsions are coated upon paper, hydrophobic polymer coated paper or film supports. Paper coated with polyolefins is especially useful as a support for the emulsions. Representative colloid vehicles for the emulsion layers are gelatin and other naturally occurring hydrophilic organic colloids as well as hydrophilic synthetic polymers such as polyvinyl alcohol, cellulose ethers and partially hydrolyzed cellulose esters. The silver halide may, for example, be silver chloride or silver bromide or mixtures of these silver halides. Silver iodide can also be present. The conventional silver halide developing agents, such as hydroquinone and its derivatives or a 3-pyrazolidone, used for developing the emulsion layer can be present in the emulsion layers, in which case development is carried out with alkaline solutions. Otherwise, the developing agents are contained in the alkaline developer solutions as usual.

The transparent polymeric sheet which is laminated to the thiocyanate stabilized emulsion surfaces includes a support of desired thickness, e.g. about 2 to 10 mils thick, of hydrophobic organic colloid such as cellulose organic acid esters and linear polyesters. Cellulose acetate and polyethylene terephthalate are especially useful. The hydrophilic organic colloid vehicle of the layer coated on the transparent sheet is similar or identical to the organic colloid vehicle of the silver halide emulsion layer to which it is to be laminated. Different hydrophilic organic colloids can be used to the extent they are compatible. Gelatin is a preferred hydrophilic organic colloid vehicle. t

In preparing the transparent sheets anaqueous solution of the hydrophilic organic colloid such as gelatin is prepared containing the heavy metal salt such as zinc acetate. The solution is prepared and coated'upon the transparent support so. I

that sufficient hydrophilic organic colloid such as gelatin is present to cause the layer to adhere to the thiocyanate stabilized emulsion surface and sufficient to carry the metal salt. In the case of gelatin about 0.5 to 5 grams per square foot isuseful, and in the case of zinc salts like zinc acetate dihydrate about 15 to 150 mg. per square foot calculated as zinc is adequate. It can be expected that the optimum amounts of the different heavy metal salts will vary with their effectiveness to stabilize the silver images. Representative heavy metal salts used are water-soluble salts of zinc, cadmium, lead, germanium, magnesium, zirconium and tin. The anion of the salt is, for

example, acetate, formate, nitrate or sulfate. However, the metal salt selected should not interfere with the adhesion of the hydrophilic layer to the emulsion layer containing the silver irnagel-For example, zirconium salts are less preferred when gelatin is usedsince these salts tend to harden gelatin and reduce adhesion to the emulsion surface. Zirconium salt can be used with other colloid vehicles such as hydrolyzed cellulose ester.

The following examples will serve to illustrate my invention.

EXAMPLE 1 A A photographic paper comprising a paper base carrying a gelatin-silver chlo'r'obromide emulsion layer containing hydroquinone is given a step tablet exposure and developed about 2.5 seconds with an alkaline activator solution having the formula:

50 grams Sodium hydroxide 40 grams Potassium bromide 2 grams Water to 1 liter Without washing, the emulsion layer is treated for about 4 seconds withthe following thiocyanate stabilization solution and the excess solution quickly removed, e.g. by squeegeeing.

Ammonium thiocyanate 300.0 grams Aceuoacid; glacial 83.9 grams Sodium acetate 30.0 grams Aluminum sulfate (25% AI ISOJ, aqueous solution) I 10.0 grams 1.2.4-rriazoIe-3-thinl 1.0 gram Water to liter The print is then incubated at 120 F., percent RH for 1-8 days to test for image stability with the following results:

REFLECTION DENSITY READINGS Step Fresh 1 Day 2 Day 4 Day 8 Day 5 L51 I.I0 1.06 1.00 1.00

B. The process of A is carried out except after the stabilization treatment a polyester film base 4 mils thick coated with a layer of 1 gram gelatin per square foot is laminated with moderate pressure to the emulsion layer still moist with the stabilization solution and the sandwich incubated with the following results:

REFLECTION DENSITY READINGS Step Fresh 1 Day 2 Day 4 Day 8 Day C. The process of B is carried out except the polyester sheet carries a layer of 2 grams gelatin per square foot and 370 mg. per square foot of zinc acetate dihydrate. When this layer is laminated to the moist silver print and incubated, the results are as follows:

REFLECTION DENSITY READINGS Step Fresh 1 Day 2 Day 4 Day 8 Day The surface is glossy and the silver image is clearly visible through the polyester base.

It is apparent that in test B the lamination of the simple gelatin layer to the silver image aided in stabilizing the silver image. However, in the process of the invention represented by test C, in the presence of the zinc salt there was appreciably less loss in silver density during incubation.

EXAMPLE 2 laminated to the gelatin layer containing the zinc salt, very good stability to light, heat and moisture is obtained. The image has high definition and the surface is glossy.

The processes of the above examples can be carried out using other thiocyanate stabilization compositions, for example containing ammonium thiocyanate and a mercaptan such as a mercaptoazole as disclosed in Belgian Pat. No. 639,140 and French Pat. No. 1,335,294 wherein l-substituted-S-mercaptotetrazoles such as 1-phenyl-5-mercaptotetrazole are used. Case, US. Ser. No. 727,714, filed May 8, 1968 can be referred to for a useful stabilization formula containing adipic or succimc acids. thiocyanate and, if desired, a mercaptan compound.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

I claim 1. In a photographic stabilization process wherein a developed photogra hic emulsion layer containing a silver image 18 stabilized y treatment with a solution containing thiocyanate and a mercaptan, the improvement for increasing the stability of the silver image and protecting the surface of the photographic layer, comprising laminating the surface of a hydrophilic organic colloid layer containing a water-soluble heavy metal salt and adhered to a transparent support, to the surface of said photographic layer in the presence of moisture.

2. The process of claim 1 wherein the heavy metal salt is a zinc salt.

3. The process of claim 1 wherein from about 15 to mg. of zinc acetate dihydrate per square foot calculated as zinc is present in the organic colloid layer.

4. The process of claim 2 wherein the developed emulsion layer is coated upon a paper support.

5. The process of claim 4 wherein the developed emulsion layer is coated upon a film support.

6. The process of claim 2 wherein the developed emulsion layer is coated on a surface of a hydrophobic polymer coated paper support.

7. A sheet for lamination to the surface of a thiocyanate stabilized silver halide emulsion layer containing a silver image, comprising a transparent, hydrophobic polymeric support and a hydrophilic organic colloid layer containing about 15 to 150 mg. of a water-soluble zinc salt per square foot calculated as zinc adhered to the surface of said support.

8. A photographic element comprising a support, a layer thereon containing a thiocyanate and mercaptan stabilized silver image and a hydrophilic organic colloid layer containing a water-soluble heavy metal salt on a transparent support adhered to said first-mentioned layer. 

2. The process of claim 1 wherein the heavy metal salt is a zinc salt.
 3. The process of claim 1 wherein from about 15 to 150 mg. of zinc acetate dihydrate per square foot calculated as zinc is present in the organic colloid layer.
 4. The process of claim 2 wherein the developed emulsion layer is coated upon a paper support.
 5. The process of claim 4 wherein the developed emulsion layer is coated upon a film support.
 6. The process of claim 2 wherein the developed emulsion layer is coated on a surface of a hydrophobic polymer coated paper support.
 7. A sheet for lamination to the surface of a thiocyanate stabilized silver halide emulsion layer containing a silver image, comprising a transparent, hydrophobic polymeric support and a hydrophilic organic colloid layer containing about 15 to 150 mg. of a water-soluble zinc salt per square foot calculated as zinc adhered to the surface of said support.
 8. A photographic element comprising a support, a layer thereon containing a thiocyanate and mercaptan stabilized silver image and a hydrophilic organic colloid layer containing a water-soluble heavy metal salt on a transparent support adhered to said first-mentioned layer. 